U.S. patent number 5,786,631 [Application Number 08/539,188] was granted by the patent office on 1998-07-28 for configurable ball grid array package.
This patent grant is currently assigned to LSI Logic Corporation. Invention is credited to Clifford R. Fishley, Michael L. Lofstedt.
United States Patent |
5,786,631 |
Fishley , et al. |
July 28, 1998 |
Configurable ball grid array package
Abstract
A configurable package for mounting an integrated circuit to a
circuit board. The package has a substrate for receiving the
integrated circuit. On the substrate are contacts for making
electrical connections between the substrate and the integrated
circuit. The substrate also has solder balls for making electrical
connections between the substrate and the circuit board. Each one
of the contacts is in electrical contact with one each of the
solder balls. A clip ring/dam ring overlays and attaches to the
substrate. The clip ring/dam ring forms a reservoir for receiving
the integrated circuit on the substrate. Also, formed at the
periphery of the clip ring/dam ring, are clamping tabs. The
reservoir can be filled with an encapsulating material, such as
epoxy, to complete the package. A lid is provided for covering the
integrated circuit. A clip overlays the lid and releasably attaches
to the clamping tabs of the insert, and retains the lid to the
insert. The lid may have fins formed in it, to act as a heat sink,
and dissipate heat by convection to air flowing within the
environment.
Inventors: |
Fishley; Clifford R. (San Jose,
CA), Lofstedt; Michael L. (Tracy, CA) |
Assignee: |
LSI Logic Corporation
(Milpitas, CA)
|
Family
ID: |
24150172 |
Appl.
No.: |
08/539,188 |
Filed: |
October 4, 1995 |
Current U.S.
Class: |
257/701;
257/E23.086; 257/E23.004; 257/787; 257/E23.069 |
Current CPC
Class: |
H01L
23/4093 (20130101); H01L 23/49816 (20130101); H01L
23/13 (20130101); H01L 2224/48227 (20130101) |
Current International
Class: |
H01L
23/13 (20060101); H01L 23/40 (20060101); H01L
23/48 (20060101); H01L 23/34 (20060101); H01L
23/498 (20060101); H01L 23/12 (20060101); H01L
023/12 () |
Field of
Search: |
;257/787,780,790,701 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Thomas; Tom
Assistant Examiner: Potter; Roy
Attorney, Agent or Firm: Luedeka, Neely & Graham,
P.C.
Claims
What is claimed is:
1. A configurable package for mounting an integrated circuit to a
circuit board comprising:
a substrate for receiving the integrated circuit, the substrate
having contacts for making electrical connections between the
substrate and the integrated circuit, and solder balls for making
electrical connections between the substrate and the circuit board,
each one of the contacts being in electrical contact with one of
the solder balls, and
a clip ring/dam ring for overlaying and attaching to the substrate
to stiffen and reinforce the substrate, the clip ring/dam ring
forming a reservoir for receiving the integrated circuit on the
substrate, the clip ring/dam ring forming attachment members for
making attachments thereto.
2. The package of claim 1 further comprising an epoxy seal situated
within the reservoir of the clip ring/dam ring for protecting the
integrated circuit.
3. The package of claim 1 wherein the attachment members comprise
tabs formed at the periphery of the clip ring/dam ring.
4. The package of claim 1 further comprising:
a lid for covering the integrated circuit received and the
reservoir formed by the substrate and the clip ring/dam ring,
and
a clip for releasably attaching the lid to the attachment members
of the clip ring/dam ring, and for retaining the lid to the clip
ring/dam ring thereby.
5. The package of claim 4 wherein the lid further comprises a heat
dissipative material.
6. The package of claim 4 wherein the lid has fins formed
therein.
7. The package of claim 4 wherein the clip further comprises:
hooks for engaging the attachment members of the clip ring/dam
ring,
compression points for receiving the lid covering the integrated
circuit, and
flextures disposed between the hooks and the compression points,
for providing compression at the compression points, and for
providing tension at the hooks.
8. The package of claim 4 wherein:
the lid further comprises;
a lower surface disposed adjacent the clip ring/dam ring,
an upper surface disposed opposite the lower surface, and
fins disposed on the upper surface, for receiving heat from the lid
and dissipating the heat so received, and;
the clip further comprises;
hooks for engaging the attachment members of the clip ring/dam
ring,
compression points for receiving the upper surface of the lid,
flextures disposed between the hooks and the compression points,
for providing pressure at the compression points, and for providing
tension at the hooks, and
a cut-out formed in the clip, for allowing the fins disposed on the
upper surface of the lid to extend through the clip.
9. The package of claim 4 wherein the lid is rotatable to a
plurality of different positions in respect to the clip ring/dam
ring.
10. The package of claim 4 further comprising an integrated circuit
disposed between the substrate and the lid and having electrical
connection to the contacts of the substrate.
11. The package of claim 1 wherein the clip ring/dam ring further
comprises:
down-turned lips at the periphery of the clip ring/dam ring,
slots at the periphery of the clip ring/dam ring, which define tabs
incorporating the down-turned lips,
a center void defined by up-turned interior lips for forming the
reservoir,
the clip ring/dam ring having a greater circumference than the
substrate, and extending outwardly over the substrate, with the
tabs disposed beyond the periphery of the substrate, and
the down-turned lips on the tabs disposed above the circuit board
on which the substrate is mounted.
12. A package according to claim 1 further comprising a
semiconductor device mounted to the substrate.
13. A clip ring/dam ring for a ball grid array package having a dam
ring for forming a reservoir, for receiving an integrated circuit,
and slots forming clamping tabs at the periphery of the clip
ring/dam ring for making clamping connections thereto.
14. The clip ring/dam ring of claim 13 further comprising:
down-turned lips at the periphery of the clip ring/dam ring,
and
the dam ring defined by up-turned interior lips for forming the
reservoir.
15. A configurable package for mounting an integrated circuit to a
circuit board comprising:
substrate means having a top surface and an opposing bottom
surface, for receiving the integrated circuit,
first connector means disposed on the top surface of the substrate
means, for making electrical connections between the substrate
means and an integrated circuit,
second connector means disposed on the bottom surface of the
substrate means, for making electrical connections between the
substrate means and the circuit board,
interconnect means disposed within the substrate means, for making
electrical connections between the first connector means and the
second connector means,
clip ring/dam ring means attached to the top surface of the
substrate means, for stiffening the substrate means,
reservoir means formed within the clip ring/dam ring means, for
receiving the integrated circuit, and
attachment means formed on the clip ring/dam ring means, for making
attachments thereto.
16. The package of claim 15 further comprising:
lid means for covering the integrated circuit received by the
reservoir means, and
clip means for releasably attaching the lid means to the attachment
means, and for retaining the lid to the clip ring/dam ring means
thereby.
17. The package of claim 15 further comprising:
lid means for covering the integrated circuit received by the
reservoir means, the lid means having;
a lower surface disposed adjacent the clip ring/dam ring means,
an upper surface disposed opposite the lower surface, and
heat dissipation means disposed on the upper surface, for receiving
heat from the lid means and dissipating the heat so received;
and
clip means for releasably attaching the lid means to the attachment
means, and for retaining the lid to the clip ring/dam ring means
thereby, the clip means having;
hook means for engaging the attachment means, compression point
means for receiving the upper surface of the lid means,
flexture means disposed between the hook means and the compression
point means, for providing compression at the compression points,
and for providing tension at the hook means, and
cut-out means formed in the clip means, for allowing the heat
dissipation means on the upper surface of the lid means to extend
through the clip means.
18. The package of claim 15 wherein the clip ring/dam ring means
further comprises:
down-turned lip means disposed in a down-turned fashion at the
periphery of the clip ring/dam ring means,
slot means at the periphery of the clip ring/dam ring means, which,
together with the first lip means, define the attachment means,
up-turned lip means disposed in an up-turned fashion at the
interior of the clip ring/dam ring means, for defining the
reservoir means,
the clip ring/dam ring means having a greater circumference than
the substrate means, and extending outwardly over the substrate,
with the attachment means disposed beyond the periphery of the
substrate means, and
the down-turned lip means on the attachment means disposed above
the circuit board on which the substrate means is mounted.
19. A configurable package for mounting an integrated circuit to a
circuit board comprising:
a substrate for receiving the integrated circuit, the substrate
having contacts for making electrical connections between the
substrate and the integrated circuit, and solder balls for making
electrical connections between the substrate and the circuit board,
each one of the contacts being in electrical contact with one of
the solder balls, and
a clip ring/dam ring for overlaying and attaching to the substrate
to stiffen and reinforce the substrate, the clip ring/dam ring
forming a reservoir for receiving the integrated circuit on the
substrate, the clip ring/dam ring forming attachment members for
making attachments thereto, the clip ring/dam ring having;
down-turned lips at the periphery of the clip ring/dam ring,
slots at the periphery of the clip ring/dam ring, which define tabs
incorporating the down-turned lips,
a center void defined by up-turned interior lips for forming the
reservoir,
the clip ring/dam ring having a greater circumference than the
substrate, and extending outwardly over the substrate, with the
tabs disposed beyond the periphery of the substrate, and
the down-turned lips on the tabs disposed above the circuit board
on which the substrate is mounted;
an epoxy seal situated within the reservoir of the clip ring/dam
ring for protecting the integrated circuit,
a lid for covering the integrated circuit received and the
reservoir formed by the substrate and the clip ring/dam ring, the
lid formed of a heat dissipative material, and having;
a lower surface disposed adjacent the clip ring/dam ring,
an upper surface disposed opposite the lower surface, and
fins disposed on the upper surface, for receiving heat from the lid
and dissipating the heat so received; and
a clip for releasably attaching the lid to the attachment members
of the clip ring/dam ring, and for retaining the lid to the clip
ring/dam ring thereby, the clip having;
hooks for engaging the attachment members of the clip ring/dam
ring,
compression points for receiving the upper surface of the lid,
flextures disposed between the hooks and the compression points,
for providing compression at the compression points, and for
providing tension at the hooks, and
a cut-out formed in the clip, for allowing the fins disposed on the
upper surface of the lid to extend through the clip.
Description
FIELD OF THE INVENTION
The present invention relates to the field of integrated circuit
packages, and more particularly to surface mount packages for
integrated circuits.
BACKGROUND OF THE INVENTION
Integrated circuits, which are formed on a monolithic semiconductor
or ceramic substrate, generate heat during operation. Although they
typically do not draw a relatively large amount of current, they
are often so small in terms of surface area covered, that the power
density of the circuit is quite high. Therefore, they must
dissipate a relatively large amount of heat through a relatively
small surface area. If this heat is not dissipated, the circuit can
be destroyed by the heat, and in being destroyed, the integrated
circuit can damage other components as well.
Integrated circuits are typically packaged before they are used
with other components as parts of larger electronic systems. The
packages provide electrical connections to the contact areas of the
integrated circuit, and also provide protection for the fragile
circuit. Since the package encapsulating the integrated circuit
completely surrounds the device, it must provide for some method of
heat dissipation, or it will add to the problem of heat retention
in the device.
Surface mount technology packages are especially preferred in
manufacturing because of their size, cost, and weight. A surface
mount package is designed to be attached, usually by solder or
conductive epoxy, directly to the circuit board in which the
integrated circuit is to be used. Surface mount packages eliminate
the extra steps associated with attaching a socket to the circuit
board, and then inserting a packaged device into the socket.
Obviously, by eliminating the socket itself, the size, weight, and
cost of the socket are also eliminated.
However, surface mount packages can be very difficult, if not
impossible, to reconfigure after attachment to the circuit board.
For instance, if after attachment to the circuit board it is
discovered that a different package is required for a socketed
device, the device may simply be removed from the socket, and a new
device, in a preferable package, inserted in its place. With a
surface mount package, the option to remove the device itself from
the circuit board no longer exists, as there are no separable
components that can be removed without unsoldering the package from
the board. Such a rework operation may well create more problems
than it will fix, by damaging the other circuits on the board, the
device being removed, or both.
One situation in which reconfiguring a device's package may be
desirable is when the circuit board is to be placed in an
environment which was not foreseen at the time that the package was
attached to the circuit board. For instance, a package that was
designed for a relatively cool environment may be wholly inadequate
for a warmer environment, where a package with fins or other heat
sink type apparatus would be more appropriate. Further, even if a
finned package is used on the circuit board, the direction in which
the fins are oriented may be transverse to the flow of air within
the environment, thus reducing the effectiveness of the heat
transfer from the fins to the circulating air.
While these would not be difficult problems to overcome with a
socketed device, they are quite difficult to resolve for a surface
mounted package. One solution to this situation would be to build a
given circuit board in several different configurations, each
optimized for a different environment in which the board may be
used. However, the expense to manufacture and inventory of several
versions of the same circuit is cost prohibitive for many
applications. Typically then, manufacturers have had to either use
socketed devices, with their attendant expense and other drawbacks,
or accept the reality of the reduced service life that accompanies
overheated surface mount devices.
What is needed, therefore, is a surface mount package for an
integrated circuit that provides the benefits of reduced cost,
size, and weight, but is also reconfigurable after attachment to a
circuit board. The surface mount package should individualize and
optimize the heat dissipation characteristics of the package to the
temperature and air flow conditions of the environment in which the
circuit board may be used.
SUMMARY OF THE INVENTION
The above and other needs are met by a configurable package for
mounting an integrated circuit to a circuit board. The package has
a substrate configured for receiving the integrated circuit. On the
substrate are contacts for making electrical connections between
the substrate and the integrated circuit. The substrate also has
solder balls for making electrical connections between the
substrate and the circuit board. An electrical connection is
provided between each one of the contacts and one of the solder
balls. In this manner the substrate provides for electrical
connection between the integrated circuit, which is received on the
upper surface of the substrate and the circuit board. In one
embodiment, the circuit board is attached to the lower surface of
the substrate. In an alternate embodiment the circuit board is
attached to a different portion of the upper surface of the
substrate, in a manner well known in the art.
A clip ring/dam ring overlays and attaches, preferably by adhesive
bonding, to the substrate. The clip ring/dam ring is configured to
form a reservoir for receiving the integrated circuit on the
substrate. Also formed on the clip ring/dam ring, preferably at the
periphery, are clamping tabs. If the device is to be used in a
relatively cool environment, the integrated circuit is mounted in
the reservoir and the reservoir can be filled with an encapsulating
material, such as epoxy, to complete the package. If the device is
to be used in a warmer environment, then a lid is provided for
covering the integrated circuit and reservoir. Such a lid would
preferably be made of a heat dissipative material. One or more
clips overlay the lid and releasably attach to the clamping tabs of
the clip ring/dam ring, and retain the lid to the clip ring/dam
ring. Alternately, the clip or clips are integrated into the
lid.
In an even warmer environment, the lid may have fins formed in it,
to act as a heat sink, and dissipate heat to the air flowing within
the environment. Because the clip may be released from the clip
ring/dam ring, a lid without fins may be replaced with a lid having
fins, should the circuit board be placed in a different
environment, or a finned lid can be reoriented so as to make the
most efficient use of the air circulation within the environment.
In such a case, the tabs formed on the clip ring/dam ring are
spaced and configured to attach to the clip and lid (or heat sink)
when the clip or lid are in different orientations. Preferably, the
lid or heat sink is mountable in at least two positions, with one
position being rotated ninety degrees with respect to the other.
Most preferably the lid may be oriented to an infinite number of
angular positions.
BRIEF DESCRIPTION OF THE DRAWINGS
Further advantages of the invention will become apparent by
reference to a detailed description of preferred embodiments,
particularly when considered in conjunction with the following
drawings. In the drawings like reference numerals denote like
elements throughout the several views.
FIG. 1A is a somewhat diagrammatic perspective view of an
integrated circuit attached to the upper surface of a substrate,
showing the bonding wires;
FIG. 1B is a somewhat diagrammatic perspective view of the lower
surface of the substrate, showing the solder balls.
FIG. 2A is a perspective view of the upper surface of a clip
ring/dam ring.
FIG. 2B is a perspective view of the lower surface of a clip
ring/dam ring.
FIG. 2C is a top plan view of the clip ring/dam ring, showing the
clamping tabs.
FIG. 2D is a cross-sectional view of the clip ring/dam ring.
FIG. 3A is a somewhat diagrammatic perspective view of the
integrated circuit as mounted to the substrate, with the clip
ring/dam ring overlaying the substrate.
FIG. 3B is a somewhat diagrammatic cross-sectional view of the
integrated circuit, substrate, and clip ring/dam ring.
FIG. 3C is a cross-sectional view of the integrated circuit,
substrate, and clip ring/dam ring, with an epoxy seal.
FIG. 4A is a perspective view of the upper surface of a lid.
FIG. 4B is a perspective view of the lower surface of the lid.
FIG. 4C is a diagrammatic cross-sectional view of the integrated
circuit, substrate, clip ring/dam ring, and lid.
FIG. 4D is a perspective view of the upper surface of a lid having
fins.
FIG. 4E is a perspective view of the upper surface of a circular
lid having fins.
FIG. 5A is a top plan view of a clip.
FIG. 5B is a cross-sectional view of the integrated circuit,
substrate, clip ring/dam ring, lid, and clip.
FIG. 6A is an end view of the clip showing the detail of a
hook.
FIG. 6B is an edge view of the clip ring/dam ring showing the
detail of a clamping tab.
FIG. 6C is an edge view of the clip ring/dam ring, showing the
detail of a hook engaging a clamping tab.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to FIG. 1A there is depicted a substrate 10, to which
there is attached an integrated circuit 12. The integrated circuit
12 is commonly attached with an adhesive 14, such as an epoxy, to
the upper surface 11 of the substrate 10, so that the integrated
circuit 12 is immovably attached to the substrate 10. Bonding wires
16 are used to make electrical connection between the first
connector means or bonding pads 18 of the integrated circuit 12 and
the contacts 20 of the substrate 10. As depicted in FIG. 1A there
are only eight sets of bonding pads 18, bonding wires 16, and
contacts 20. In a typical configuration, however, there may be many
more such sets present, but for the sake of clarity in the
drawings, only eight sets are depicted.
The lower surface 13 of the substrate is depicted in FIG. 1B, and
shows second connector means or solder balls 22. One of each of the
solder balls 22 is electrically connected by an electrical path
with one each of the contacts 20 on the upper surface 11 of the
substrate 10, depicted in FIG. 1A. Thus, electrical contact can be
made from the solder balls 22 to the bonding pads 18 of the
integrated circuit 12. The solder balls 22 are preferably disposed
in a grid-like arrangement about the periphery of the lower surface
13 of the substrate 10. Because so few of the solder balls 22 are
depicted, they are quite spread out in this view. However, in a
typical configuration there may be several hundred solder balls 22
placed quite close to each other, preferably disposed in several
concentric rectangular rings inside the periphery of the substrate
10.
Because of the arrangement of the solder balls 22, this type of
package configuration is referred to as a ball grid array package.
The substrate 10 acts to some degree as a heat sink to help cool
the integrated circuit 12, and also provides a convenient method of
making electrical contact between the bonding pads 18 and the other
components that will be used with the integrated circuit 12. The
substrate 10 must be of sufficient rigidity to prevent excessive
flexing of the integrated circuit 12, which would cause the
integrated circuit 12 to detach from the substrate 10 by breaking
the adhesive 14, or may even crack the integrated circuit 12.
This rigidity is typically provided by using thicker layers of
inexpensive materials, such as thermoplastic resins, or more
expensive materials, such as ceramics. As the ceramics tend to be
somewhat brittle, thicker layers of ceramic are required to ensure
the structural stability of the substrate 10. The present invention
provides for the use of thinner substrates 10, by providing for the
required rigidity in another manner, as described more fully
below.
In FIG. 2A there is depicted a clip ring/dam ring 24. On the upper
surface 26 of the clip ring/dam ring 24 is formed a rectangular dam
ring 28, which has the form of up-turned lips and which defines a
center void or reservoir 30. Formed at the periphery of clip
ring/dam ring 24 are slots 32, defining attachment members or
clamping tabs 34, the purpose of which will be explained in greater
detail below. The lower surface 36 of the clip ring/dam ring 24 is
depicted in FIG. 2B, and shows retaining lip 38 which has the form
of down-turned lips, the inside surface of dam ring 28, and the
reservoir 30. Also visible are the lower surfaces of the clamping
tabs 34, which form an angle with the retaining lip 38. FIG. 2C is
a top plan view of the clip ring/dam ring 24, and shows a
preferable flat 40 which may aid in orienting the package when
mounted on a circuit board. FIG. 2D is a cross-sectional view of
the clip ring/dam ring 24 along line A--A of FIG. 2C.
The clip ring/dam ring 24 is preferably made of a relatively
inexpensive material, such as copper or a high temperature,
light-weight plastic, or any other material that is heat conductive
and rigid. The clip ring/dam ring 24 is placed over the substrate
10 as depicted in FIG. 3A. The integrated circuit 12 is received by
and situated within the reservoir 30 formed by the damn ring 28.
FIG. 3B shows a cross-section of the structure of FIG. 3A along
line B--B, and provides a view of the adhesive 14 which is used to
attach the integrated circuit 12 to the substrate 10. Also visible
are the interconnect means or connections 42 which connect the
contacts 20 to the solder balls 22.
The lower surface 36 of the clip ring/dam ring 24 is attached to
the upper surface 11 of the substrate 10, such as by an adhesive
41. The clip ring/dam ring 24 may, as shown, also overhang the
substrate 10 at the periphery of the structures. The retaining lip
38 of the clip ring/dam ring 24 hangs down below the upper surface
11 of the substrate 10. In the preferred embodiment, the entire
retaining lip 38 does not hang down as far as the lower surface 13
of the substrate 10. In alternate embodiments, portions of the
retaining lip 38 do hang down past the lower surface 13 of the
substrate 10, to a depth such that the weight of the completed
package will not adversely affect the mounting of the package to a
circuit board, as explained in more detail below.
Because the clip ring/dam ring 24 is rigid, the substrate 10 is not
required to provide rigidity to the completed package, and may thus
be fashioned of thinner materials, and from a wider variety of
materials, which may be chosen for their other attributes, such as
cost, heat conductance, and ease of manufacture, rather than
rigidity.
If the integrated circuit 12 is to be used in an environment where
adequate heat dissipation from the device will not be a problem,
the reservoir 30 can be filled with an encapsulating material, such
as epoxy 44, as depicted in FIG. 3C. The dam ring 28 keeps the
epoxy 44 in the reservoir 30, and prevents the spread of the epoxy
44 to other portions of the package. When the epoxy 44 is cured,
the package is completed, and ready for surface mounting to a
circuit board.
If the integrated circuit 12 is to be used in a warmer environment,
where heat dissipation will be more of a consideration and an epoxy
encapsulation may not provide sufficient cooling for the device, a
lid 46, such as that depicted in FIGS. 4A and 4B, can be used to
protect the integrated circuit 12. The lid 46 preferably forms a
recess 48, to reduce air volume within the reservoir 30 when the
lid 46 is attached to the clip ring/dam ring 24. FIG. 4B shows side
wall 50 of the lid 46. The lid 46 is preferably made of a heat
dissipative material such as metal, ceramic, or plastic.
The lid 46 efficiently conducts heat from the lower surface 49 of
the lid 46, which is nearer the integrated circuit 12, to the upper
surface 47 of the lid 46, which is on the outside of the package.
In a preferred embodiment a compliant, thermally conductive
compound, such as thermal grease, may be placed between the
integrated circuit 12 and the lower surface 49 of the lid 46, so as
to provide for enhanced heat exchange between the integrated
circuit 12 and the lid 46.
The lid 46, depicted in cross-section in FIG. 4C in an alternate
embodiment without a recess 48, overlays the clip ring/dam ring 24
and may be attached to the clip ring/dam ring 24 such as by an
adhesive 52 between the side walls 50 of the lid 46 and the upper
surface 26 of the clip ring/dam ring 24. However, if the lid 46 is
attached by adhesive 52, then the lid 46 will not be able to be
removed from the clip ring/dam ring 24 at a later time. If the
temperature and air flow properties of the environment in which the
device will be used are known, and will not change, then this is an
acceptable method of attaching the lid 46. This embodiment still
provides the benefit of using a less rigid and less expensive
substrate 10, because of the use of the clip ring/dam ring 24.
If it is possible that the device will be used in a still warmer
environment, then a lid 46 such as that depicted in FIG. 4D may be
used. In this embodiment, lid 46 has a plurality of fins 54 formed
on the upper surface 47. The lid 46 and fins 54 act as a heat sink
to the integrated circuit 12, providing an increased surface area
through which the heat received by the lid 46 and fins 54 can be
radiated and convected away from the device.
The lid 46 is preferably formed in a symmetrical fashion, such as
in a square, as depicted in FIG. 4D, or a circle, as depicted in
FIG. 4E, so that the fins 54 can be oriented in a direction that
will optimize the transfer of heat to the air within the
environment wherein the package will be placed. For a lid 46 with a
square configuration, the fins 54 may be oriented in one of two
different directions. For a lid 46 with a circular configuration,
the fins 54 may be oriented in any number of different directions.
Orienting the fins 54 to the direction of air flow within the
environment is important, as optimum heat transfer will only occur
when the fins 54 are oriented such that the air flows down the
length of the fins 54. Air flow transverse to the fins 54 will
decrease the efficiency of heat transfer.
If the temperature and air patterns of the environment in which the
device is to be used are not known, then it would not be preferable
to use the adhesive 52 to attach any particular lid 46, because it
would not be known whether a finned or unfinned lid 46 would be
required, or even in what direction to orient the fins 54, if
present. Therefore, another means of attaching the lid 46 is
employed. In FIG. 5A, for example, there is depicted a clip 56,
having hooks 58 at the end of flextures 60. Also visible are
compression points 62, and cut-out 64.
As shown in FIG. 5B, the clip 56 is attached to the clip ring/dam
ring 24 and retains the lid 46 to the clip ring/dam ring 24. The
hooks 58 engage the clamping tabs 34 of the clip ring/dam ring 24,
and are kept from slipping off by the retaining lip 38. The
flextures 60 of the clip 56 provide tension to the hook 58/tab 34
assembly, to keep them engaged. The flextures 60 also provide
compression through the compression points 62 to the lid 46,
retaining it against the clip ring/dam ring 24.
Because the flextures 60 can be repeatedly compressed, the clip 56
can be removed as required to replace, for example, a plain lid 46
with a lid 46 having fins 54, should the temperature of the
environment change. Further, the fins 54 of a lid 46 can be
reoriented at any time, by removing the clip 56, reorienting the
lid 46, and thereby the fins 54, and replacing the clip 56. The
cut-out 64 allows the fins 54 of the lid 46 to extend through the
clip 56. Thus the clip 56 does not preclude the use of a finned lid
46, or inhibit the air flow through the fins 54.
Another advantage of the present invention is realized because the
clip 56 is removable. In some circumstances the weight of the
finned lid 46 impairs the process of mounting the device to the
circuit board. Because the finned device weighs more than a device
without fins, the solder balls 22 may flatten excessively during
the mounting process. This can result in reduced adhesion between
the package and the circuit board, or in electrical bridging
between the solder balls 22, if they flatten to the extent that
they make contact one with another.
However, if portions of the retaining lip 38 hang down past the
lower surface 13 of the substrate 10 as explained above, then the
weight of the completed package is less of a consideration, as the
retaining lip 38 will prevent the weight of the completed package
from impairing the mounting of the package to the circuit board. In
addition, because the clip 56 and finned lid 46 are removable, the
finned lid 46 can be removed during the mounting process, and then
replaced on the package when the mounting process is completed.
In FIG. 6A there is depicted an end view of one of the hooks 58 of
the clip 56, showing slot 66 and side members 68. FIG. 6B depicts
the edge of the clip ring/dam ring 24, showing the detail of a
clamping tab 34. FIG. 6C depicts in greater detail how clamping tab
34 engages and retains hook 58. The slot 66 of the hook 58 has a
width and depth sufficient to receive clamping tab 34. The slots 32
of the clip ring/dam ring 24 are sufficiently wide to receive the
side members 68 of hook 58. After the clamping tab 34 is inserted
through the slot 66 of hook 58, hook 58 is raised up by flextures
60 (not depicted), and held in place by retaining lip 38 (not
depicted).
While preferred embodiments of the present invention are described
above, it will be appreciated by those of ordinary skill in the art
that the invention is capable of numerous modifications,
rearrangements and substitutions of parts without departing from
the spirit of the invention, such as by using the invention with
various package types, such as enhanced plastic ball grid array
packages, ceramic ball grid array packages, and tape ball grid
array packages. Additionally, the invention is equally applicable
to packages designed for either wire-bonded or flip-chip
semiconductor devices.
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